The pair were tested internally by the Pakistan Cricket Board as part of their requirements prior to the tournament in India.

Pakistan were due to play their first game against Sri Lanka in Jaipur tomorrow but neither player will now take any part in the competition.

International Cricket Council chief executive Malcolm Speed said on BBC Radio: "They were tests conducted by the PCB three weeks ago. They do this before each event. They weren't recreational drugs but that is all I can say at this stage."

Drugs in sport have become a huge issue in recent years but Speed insisted: "Cricket is generally regarded as a low-risk sport. The risk for cricket would be a player injured taking a substance inadvisedly to come back quickly."

The news comes after a turbulent couple of months for Pakistan cricket following The Oval ball-tampering fiasco, board upheaval and the resignation and re-appointment of Younis Khan as stand-in captain.

Shoaib and Asif are two of Pakistan's most potent weapons and made a huge difference to the side towards the end of the tour of England this summer after overcoming injury.

As a result of the test results, Pakistan have cancelled a training session for this morning and are due to make a statement at 8am BST.

The ICC have signed up to the World Anti-Doping Agency's code and the players could face hefty bans.

Speed said: "We take a zero-tolerance approach to drugs. We are disappointed this has happened and disappointed for these players. We will get to the bottom of it."

Khan admitted the news was a surprise but insisted th team would try to concentrate on tomorrow's match.

He told Indian station NDTV: "Yes it is obvious that when your key players are forced out it is a shock, but we just have to get on and play well, putting all else out of our mind."

Coach Bob Woolmer added: "The events have happened very fast. We haven't been able to discuss this as a team yet, we will do so this evening.

"Our job is to put behind us all the distractions and concentrate on playing the game tomorrow against Sri Lanka. We want to make sure we get the two points."

England batsman Andrew Strauss says there is no place for drugs in cricket and any positive findings would have be dealt with harshly.

Strauss told BBC Radio Five Live: "When drugs are used in any sport it is not a great day for that sport and this not a great day for cricket.

"The process has got to be gone through and proved. That is the situation and if bans are in place that has got to happen I think.

"I don't think it is very common in cricket. I have not heard of it in any team I have been playing in."